1. Element for Legacy Indication
January 2002
doc.: IEEE /068r0
January 2002
Element for Legacy Indication
802.11g introduces the need for a BSS to indicate the presence of legacy stations (either associated to, or in the vicinity of the BSS). This enables stations to make optimal decisions on whether RTS/CTS (or other protection mechanisms) are needed for OFDM frames.
Tim Godfrey, Intersil
Tim Godfrey, Intersil

2. Need for the new element
January 2002
doc.: IEEE /068r0
January 2002
Need for the new element
802.11g stations need to know if any legacy stations are associated in the BSS. If no legacy stations are associated, the g stations do not need to use protection mechanisms for OFDM frames.
The AP keeps track of associated stations, and knows (by their capability information bits) whether they are g stations or legacy stations.
Legacy stations will not understand this new element, and will ignore it.
Tim Godfrey, Intersil
Tim Godfrey, Intersil

3. Element Definition A new element is defined, with one octet value.
January 2002
Element Definition
A new element is defined, with one octet value.
The octet contains two 1-bit fields.
B0 is set to 1 if any b stations are associated
B1 is optional. It is set to the same value as bit 0 unless optional, additional information is provided.
This bit may be used by “smart” APs that implement techniques to provide additional information to stations.
“r” bits are reserved. B0 B7
One Octet
Element ID
Length =1 B0 B1 r
Tim Godfrey, Intersil

4. January 2002
Mandatory Functions
An g conformant AP must generate this element.
The AP must set bit 0 to a “0” if no b stations are associated. The AP must set bit 0 to a “1” if any b stations are associated.
If the AP is not providing additional information, it must set bit 1 to the same value as bit 0.
There is no mandatory behavior for a station. It may or may not make use of this element.
The recommended use of this information is to indicate the station should use protection mechanisms (such as RTS / CTS) for OFDM frames.
Tim Godfrey, Intersil

5. January 2002
Use of Bit 1
Bit 1 must be set to the same value as bit 0, unless additional information is conveyed through the following encoding:
Bit 0
Bit 1
Meaning 1
No b legacy stations are associated, but the AP recommends the use of protection mechanisms (possibly because legacy frames from another BSS have been received by the AP)
802.11b legacy stations are associated, but the AP suggests that protection mechanisms are not necessary currently, possibly because the legacy stations have all been “quiet” (perhaps in power save).
Tim Godfrey, Intersil

6. January 2002
Normative Text
Add a new clause to (7.3.2.last+1) containing the following text:
The legacy indication element provides stations with an indication of the presence of legacy stations in the BSS. See Figure xx. Stations may use this information to control their use of protection mechanisms (such as RTS / CTS) for OFDM frames. An Access Point shall generate this element in each Beacon Frame. The AP shall set bit 0 to a “0” if no b stations are associated. The AP shall set bit 0 to a “1” if any b stations are associated. The AP shall set bit 1 to the same value as bit 0 unless it is providing additional, optional information. If optional information is provided, it shall be according to this table:
The editor is requested to assign a unique element ID.
Bit 0
Bit 1
Meaning 1
No b legacy stations are associated, but the AP recommends the use of protection mechanisms
802.11b legacy stations are associated, but the AP suggests that protection mechanisms are not currently needed.
Figure xx: Legacy Indication Element
Element ID
Length =1 b0 b1 r B0 B7
One Octet
Tim Godfrey, Intersil

7. January 2002
Motion
Instruct the editor to incorporate the text in document 02/*** slide 6 into the draft.
Tim Godfrey, Intersil